Spherical segment electrode imaging chamber

ABSTRACT

An imaging chamber for an electron radiography system, including spaced spherical electrodes defining a gas gap therebetween. An arrangement for clamping the receptor sheet and stretching it to a spherical configuration against one of the electrodes. A plurality of clamp strips disposed about one electrode and spring loaded toward the other electrode, with the other electrode being moveable toward the first electrode to clamp the receptor sheet at the clamp strips and then move the clamp strips against the spring load to stretch the clamped receptor sheet.

United States Patent 1191- Morsell Aug. 6, 1974 SPHERICAL SEGMENTELECTRODE IMAGING CHAMBER Primary Examiner-William F. Lindquist [75].Inventor: Arthur Lee Morsell, Tarzana, Calif. $32 25 Agent or Flrm HamsKern wane & [73] Assignee: Xonics, Inc., Van Nuys, Calif. 22 Filed: Aug.31, 1973 h be d, h

Imaging c am r or an e ec ron ra tograp y sys- [211 Appl' 3932419 tem,including spaced spherical electrodes defining a gas gap therebetween.An arrangement for clamping 52 us. Cl. 250/315, 250/379, 313/100 thereoeptorsheetand Stretching itto aspherieal [511 1m. C1..I.1T..i1i....'..;"..;.III603517726 figuration, against one of theeleotrodes- A plurality of [58] Field of Search 250/315, 315 A, 374,379, clamp Stops dlsposed about one eleotrooe and sp g 250 332; 313 100loaded toward the other electrode, with the other electrode beingmoveable toward the first electrode to [55] R f n Cit d clamp thereceptor sheet at the clamp strips and then UNITED STATES PATENTS movethe clamp strips against the spring load to stretch the clamped receptorsheet. 3,766,385 l0/l973 Morsell et a] 250/315 3,774,029 l1/l973 Muntzet al 250/315 8 Claims, 7 Drawing Figures 6/7.: SUPPL 5 pa W52 SHPPL 5PATENTEI] 5 74 saw 2 ur 3 1 SPHERICAL SEGMENT ELECTRODE IMAGING CHAMBERThis invention relates to electron radiography and in particular, to anew and improved imaging chamber. In electron radiography or ionography,an x-ray opaque gas is utilized between two electrodes in an imagingresolution loss in the images produced by conventionalelectronradiographic devices results from the fact that the x-raysentering the planar imaging chamber are parallel to the electric fieldin the gas gap only at one point (the center of the image if the x-raysource is positioned directly over the center of the imaging chamber).The angle between the incoming x-ray and the electric field can beappreciable at the edges of the image, with the result that electrons orions formed in the gas gap along a well defined ray will spread out asthey travel to the receptor surface along the electric field lines. Thisproblem is discussed in detail in copending application Ser. No.3l9,999, filed Jan. 2, 1973, entitled lonography Imaging Chamber andassigned to the assignee as the present application. Reference may bemade to said copending application for a further dis cussion of theproblem and a description of one solution utilizing complex electrodeconstruction which produces a spherical electric field in a planar gasgap. Also, it is recognized that the severity of the resolution loss canbe reduced by decreasing the gap thickness, but there is an accompanyingloss in quantum efficiency in system operation which ordinarily isundesirable.

The conventional imaging chamber has utilized flat or cylindricalelectrodes because the receptor sheet must be mounted on one of theelectrodes during exposure. The present invention provides sphericalelectrodes in the imaging chamber and an arrangement for mounting thenormally flat receptor sheet on one electrode. The spherical electrodesystem will eliminate the loss of resolution encountered in the planarelectrode system, while permitting the use of larger gas gaps with theirhigher quantum efficiency. There are also certain mechanical advantagesto the system of the invention. A concave spherical shape is convenientand practical for the top of the imaging chamber through which thex-rays pass. For the preferred embodiment of the table model cassetteimaging chamber, the top of the chamber can have a radius of curvatureequal to the imageto-source distance (typically 40 inches) and theinside surface of this top can be used as one of the sphericalelectrodes.

, Accordingly, it is an object of the present invention drawings merelyshow and the description merely describes a preferred embodiment of thepresent invention which is given by way of illustration or example. Inthe drawings:

FIG. 1 is a diagrammatic view of an electron radiographic systemincorporating the presently preferred embodiment of the imaging chamber;

FIG. 2 is a plan view of the imaging chamber of FIG.

FIG. 3 is an enlarged sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is an enlarged sectional view taken along the line 4-4 of FIG. 2showing the imaging chamber in the open position;

FIG. 5 is a view similar to that of FIG. 4 showing the imaging chamberin the closed position;

FIG. 6 is an enlarged sectional view taken along the line 6-6 of FIG. 2;and

FIG. 7 is a sectional view taken along the line 77 of FIG. 6.

The system of FIG. 1 includes an x-ray source 10 and an imaging chamberor cassette 11, with an object 12 to be x-rayed positioned above theimaging chamber. The imaging chamber includes an upper housing member 14carrying an electrode 15, and a lower housing member 16 carrying anotherelectrode 17 with an insulation sheet 18 therebetween. The dielectricreceptor sheet 20 is mounted against the electrode 15. An electric fieldis established in the gap 21 between the electrodes by means of a powersupply 22 connected via line 23 to the electrode 15 and via line 24 andfeed through insulator 25 to the electrode 17. A supply of gas underpressure is provided to the gap 21 through line 26.

The system of FIG. 1 is operated in the usual manner to produce thedesired picture and the present invention is directed to the electrodeconfiguration and means for holding the receptor sheet at an electrode.

The electrodes l5, 17 have uniformly spaced spherical surfaces at thegap 21, with center coinciding with the x-ray source at 10. With thisconfiguration, the electric field in the gap is everywhere directedtoward the x-ray source, and the ions and electrons formed in the gasgap move along paths coinciding with rays from the x-ray source.

The imaging chamber 11 may be mounted in a table 30, with the rim of theupper housing member 14 resting on a lip 31 of the table.

The imaging chamber includes means for moving the lower housing member16 toward and away from the upper housing member 14 between opened andclosed positions. When in the open position, an exposed receptor sheetmay be removed and the new receptor sheet inserted. When in the closedposition, the imaging chamber is ready for an x-ray exposure. Apreferred arrangement for opening and closing the chamber is illustratedin detail in FIGS. 3-7.

Four screws 35 are threaded into the upper housing member 14 and lockedin place with keys 36. A nut 37 is threaded onto each of the screws 35,with a thrust bearing 38 positioned about the screw between the nut andthe lower housing member 16. A sprocket 39 is affixed to each nut.

Four shafts 42 are carried in the lower housing member 16 on bearings 43held in place by collars 44, with thrust bearings 45 between the shafts42 and the lower housing member 16. Each shaft 42 has 51 threaded upperportion 47 which engages a mating opening 48 in the upper housing member14. A felt pad oiler 49 may be mounted on the upper housing member 14about each of the threaded portions 47. A sprocket 50 is carried on thelower end of each of the shafts 42.

A drive sprocket 53 is mounted on a shaft 54 carried in the lowerhousing member 16. A drive chain engages the sprockets 39, 50, the drivesprocket'53, and additional idler sprockets as desired. A drive motor 56is mounted on the lower housing member 16 and isconnected to the shaft54 through a belt 57, pulley 58, slip clutch 59 and ratchet mechanism60. The imaging chamber is driven from the open position of FIGS. 3 and4 to the closed position of FIGS. -7 by energizing the motor 56 whichdrives the chain 55. The nuts 42 are rotated on the screws 47, raisingthe lower housing member 16. As the member 16 moves upward to anintermediate position, the rotating screws 47 enter the threadedopenings 48. The lowermember l6 continues its upward movement until thechamber is closed with the eight screws providing a tight clamping forcearound the periphery of the chamber. When the chamber is closed, theclutch 59 slips and prevents damage to the mechanism until the drivemotor is shut off. The ratchet mechanism 60 provides a lock up formaintaining the chamber closed after the drive motor is shut off. Thechamber is opened by releasing the ratchet mechanism and running themotor 56 in the opposite direction.

The imaging chamber of the invention includes means for clamping orgripping the receptor sheet and holding it against one of theelectrodes, here the electrode 15, as the chamber is closed. In thepreferred embodiment illustrated, a frame is provided about theelectrode 17, typically in the form of an upstanding ridge 63 on thelower housing member 16. The ridge 63 has the contour of the edge of theother electrode 15,

and a seal gasket 64 is'carried in a groove in the upper surface of theridge.

Another frame is provided around the electrode and in the preferredembodiment illustrated comprises four clamp strips 66, 67, 68, 69 alongthe four sides of the rectangular electrode. Each clamp strip has a lip72 which tapers to a point and conforms to the contour of thecorresponding edge of the electrode 15. Each clamp strip is carried on aplurality of spring mechanisms 74. Each of the spring mechanisms 74includes a screw 75 mounted in the upper housing member 14, a'sleeve 76positioned about the screw, and a spring 77 positioned about the sleevein an opening in the upper member 14. The spring 77 engages a flange 78of the clamp strip and urges the clamp strip downward against the headof the screw 75, to the position shown in FIG. 4.

A receptor sheet 80, typically an initially flat sheet of a dielectricplastic such as Mylar or Lexan is placed in the open imaging chamberresting on the ridge 63. The motor 56 is then energized to drive thelower housing member 16 upward into engagement with the upper housingmember 14. As the lower member moves upward, the seal 64 initiallyengages the lower side of the lips 72 of the clamp .strips, with thereceptor sheet therebetween. As the lower member continues to moveupward, the receptor sheet is clamped or gripped between the clampstrips and the ridge. As the lower member continues upward, the springs77 are compressed permitting a corresponding upward movement of theclamp strips bringing the upper surfaces of the lips 72 into engagementwith the electrode 50, and the receptor sheet 80 is progressivelystretched as it comes into contact with the convex surface of theelectrode 15. When the chamber is closed, the receptor sheet is clampedin place and stretched into a spherical shape against the electrode 15as shown in FIG. 5. Gas is introduced into the gap between theelectrodes by the line 26 and passage 82 in housing member 16, theelectric power supply is connected to the electrodes, and the x-rayexposure is made. The power supply is disconnected, the chamber pressureis reduced, and the chamber is opened, permitting removal of thereceptor sheet for subsequent development. A typical imaging chamber maybe in the order of 14 inches by 17 inches and when used with an x-raysource positioned at 40 inches from the gap, the receptor sheet isstretched less than 1 percent in being conformed to the sphericalconfiguration. The receptor materials presently available, such as thosementioned above, are sufficiently strong and elastic to withstand suchstretching without tearing or assuming a permanent set. When thereceptor sheet is .positioned in the open chamber, it conforms quitewell to the curved shape of the ridge 64 due to the force of gravity,although being stiff enough to clear the lower electrode. At this timethe sheet is still flat in the middle and is circularly cylindrical forsome distance inward from each corner. This sheet maintains this shapeuntil the clamp strips are engaged and the center of the sheet contactsthe upper electrode 15.

I claim:

1. In an imaging chamber for an x-ray system, the combination of:

first and second electrodes having the shape of spherical segments;

means for mounting said electrodes in spaced relation defining a gaptherebetween so that an x-ray source will be located at the sphericalcenter of said electrodes;

means for holding a charged particle receptor sheet in said gap at oneof said electrodes; and

means for maintaining a gas under pressure in the gap.

2. An imaging chamber as defined in claim I wherein said means formounting includes means for moving said first electrode toward and awayfrom said second electrode, and said means for holding includes a firstframe positioned about said first electrode,

a second frame positioned about and moveable toward and away from saidsecond electrode, and

spring means urging said second frame away from said second electrode,

with said first and second frames clamping said receptor sheettherebetween as said first electrode is moved towards said secondelectrode, and stretching said receptor sheet into the shape of aspherical segment against said second electrode as said second frame ismoved towards said second electrode against the urging of said springmeans.

3. An imaging chamber as defined in claim 2 wherein said means formoving includes a plurality of threaded members, a drive motor, andmeans coupling said motor to said threaded members.

4. An imaging chamber as defined in claim 2 wherein said means formoving includes a plurality of screws mounted with one of saidelectrodes, at corresponding plurality of mating nuts mounted with theother of said electrodes for rotation on a screw, a drive motor, and

- ried in said ridge and engageable with said receptor having lipsconforming to edges of said second electrode, with one surface of a lipengageable with said second electrode and with the opposite surface ofthe lip engageable with said receptor sheet.

7. An imaging chamber as defined in claim 6 wherein said first framecomprises a projecting ridge conforming to edges of said secondelectrode and fixed with respect to said first electrode.

8. An imaging chamber as defined in claim 7 wherein said means formaintaining includes a seal gasket carsheet at said lips.

1. In an imaging chamber for an x-ray system, the combination of: firstand second electrodes having the shape of spherical segments; means formounting said electrodes in spaced relation defining a gap therebetweenso that an x-ray source will be located at the spherical center of saidelectrodes; means for holding a charged particle receptor sheet in saidgap at one of said electrodes; and means for maintaining a gas underpressure in the gap.
 2. An imaging chamber as defined in claim 1 whereinsaid means for mounting includes means for moving said first electrodetoward and away from said second electrode, and said means for holdingincludes a first frame positioned about said first electrode, a secondframe positioned about and moveable toward and away from said secondelectrode, and spring means urging said second frame away from saidsecond electrode, with said first and second frames clamping saidreceptor sheet therebetween as said first electrode is moved towardssaid second electrode, and stretching said receptor sheet into the shapeof a spherical segment against said second electrode as said secondframe is moved towards said second electrode against the urging of saidspring means.
 3. An imaging chamber as defined in claim 2 wherein saidmeans for moving includes a plurality of threaded members, a drivemotor, and means coupling said motor to said threaded members.
 4. Animaging chamber as defined in claim 2 wherein said means for movingincludes a plurality of screws mounted with one of said electrodes, acorresponding plurality of mating nuts mounted with the other of saidelectrodes for rotation on a screw, a drive motor, and means couplingsaid drive motor to said nuts.
 5. An imaging chamber as defined in claim4 including means mounted with one of said electrodes defining aplurality of threaded openings, a corresponding plurality of secondscrews mounted in the other of said electrodes for rotation in saidopenings as said first electrode is moved toward said second electrode,and means coupling said motor to said second screws.
 6. An imagingchamber as defined in claim 2 wherein said second frame comprises aplurality of clamp strips having lips conforming to edges of said secondelectrode, with one surface of a lip engageable with said secondelectrode and with the opposite surface of the lip engageable with saidreceptor sheet.
 7. An imaging chamber as defined in claim 6 wherein saidfirst frame comprises a projecting ridge conforming to edges of saidsecond electrode and fixed with respect to said first electrode.
 8. Animaging chamber as defined in claim 7 wherein said means for maintainingincludes a seal gasket carried in said ridge and engageable with saidreceptor sheet at said lips.